The shape of the Activities button represents your workspaces, the grouping of windows on your desktop. For example, below is the shape of the Activities button if you have 3 workspaces and the second workspace is the one that it displayed right now.
<p>To learn about the many keyboard shortcuts in GNOME, open the <i>Settings</i>. At the bottom of the <b>Keyboard</b> section, choose <b>View and Customize Shortcuts</b>.</p>
<p><b><i>Persistent Storage</i></b> allows you to save some of your files and configuration in an encryptedPersistent Storage on your Tails USB stick.</p>